Continuing Adventures in Mythos and Hellgate... but what the hell is wrong with my video card?

I spent some more time in London and Uld (Mythos) late last night after watching more Carnivale: Season 2. If you haven't watched any of Carnivale... shame on you. Go rent the DVDs now. It's by far one of the most intriguing shows to have come to television in years, but didn't sustain ratings to last past 2 seasons. Just like Arrested Development... it seems the truly unique shows, nobody watches. I caught all of Season 1 of Carnivale on HBO when it aired, but got rid of cable shortly thereafter... hence I feel I in some way contributed to its failure. Anyway, it's brilliantly written and conceived show. Go watch it.

After a few episodes, I decided it was time to go loaf on my ass somewhere else so I booted up the PC. Logged into Hellgate, patched up the test center client, and logged into my Engineer for some Piccadilly Circus fun. Now, more often than not, my ATI Radeon x1560 XT (512MB AGP) does REALLY WELL with games. It's not top of the line, but even in Hellgate, or Oblivion, and other more taxing games I can get a steady 45 frames per second. However, every so often, I have a night like the one I experienced Wednesday.

That is to say, I can barely climb above 10 frames a second, usually hovering around 5. At first I thought it was my connection, but that was steady as could be. I tried Oblivion... and lo and behold, the same problem. Mythos, same thing. No amount of settings tweaking could help me. Even WoW had trouble chugging over 20 FPS, but it was the best running of the bunch, except in towns. It ran as low as 3FPS in towns. I just don't get it.

I've done everything I can to clean out my Hard Drive, it's fit as a fiddle PCWizard tells me. So I'm fairly confident something's up with my video card. All the latest drivers are installed, settings are even set to highest performance, and yet still I can't seem to get it to climb above the low end.

As I said, it's not always like this. Could it be overheating? I don't think so, as my PC is off all day until I get home, and Catalyst swears it's running at 68-71 degrees celcius. That's hot I know, but according to ATI and every other hardware site, that's normal for this card. It runs hot. What's weird, is these FPS dips don't happen all the time. It seems random. But when they do, that's it for my night. I can't play anything that requires quick key manipulation. WoW was about it, because it's at least playable at 20FPS.

If there's anyone out there who has this card, or similar problems, or greater knowledge than I on the subject (which I'm sure of), please comment and lend some advice. Because I'm tempted to swap back in my crappy ATI Radeon 9800 at times like this.

EDIT: One last thing, I've noticed that when this drop happens, the fan on the card's not running very much, nor is the PC fan. But when both kick in, and they kick in loudly, the frame rate rises temporarily to more suitable speeds. Sound like over-heating?

Anyway, thanks for reading. Had to rant there.